Sound absorbing duct with foam-filled honeycomb core for environmental control system

ABSTRACT

A duct includes a foam-filled honeycomb core structure having a tubular shape. The duct further includes an air-impermeable duct wall coupled to an exterior surface of the foam-filled honeycomb core structure.

FIELD OF THE DISCLOSURE

The present disclosure is generally related to ducts with a foam-filledhoneycomb core of an environmental control system that absorb sound.

BACKGROUND

Vehicles, such as aircraft, include environmental control systems toprovide treated air to passengers, such as conditioned air, filteredair, etc. An environmental control system generally includes ducts totransport the treated air to passengers of the vehicle. The treated airmoving within the ducts creates noise, which may decrease passengercomfort. Noise attenuating mufflers (e.g., zone mufflers) are often usedto reduce (e.g., absorb) the noise generated by the moving air. Forexample, a muffler encases a duct of the environmental control systemand attenuates noise using insulation and/or chambers. However, noiseattenuating mufflers add weight, volume, and cost to environmentalcontrol systems. In high performance vehicles, such as aircraft,increased weight and volume increases costs and decreases performance.

SUMMARY

In a particular implementation, a duct includes a rigid air-permeabletube of composite material. The duct also includes a layer of insulationcoupled to an exterior surface of the rigid air-permeable tube. The ductfurther includes a non-rigid insulation layer in contact with the layerof insulation. The non-rigid insulation layer forms an air-impermeableduct wall.

In another particular implementation, a duct includes a rigid tube ofcomposite material. The duct also includes an insulation layer disposedwithin the rigid tube. The duct further includes a biasing memberdisposed within the rigid tube. The biasing member is configured torestrain the insulation layer against an interior surface of the rigidtube.

In a particular implementation, a method of manufacturing a ductincludes applying insulation to an exterior surface of a rigidair-permeable tube of composite material to form a layer of insulationon the exterior surface of the rigid air-permeable tube. The methodfurther includes applying non-rigid insulation to an exterior surface ofthe layer of insulation to form a non-rigid insulation layer in contactwith the layer of insulation, the non-rigid insulation layer forming anair-impermeable duct wall.

In another particular implementation, a method of manufacturing a ductincludes inserting insulation into a rigid tube of composite material toform a layer of insulation within the rigid tube. The layer ofinsulation is in contact with an inner surface of the rigid tube. Themethod further includes inserting a biasing member into the rigid tubeof composite material to secure the layer of insulation within the rigidtube.

In yet another particular implementation, a duct includes a foam-filledhoneycomb core structure having a tubular shape. The duct furtherincludes an air-impermeable duct wall coupled to an exterior surface ofthe foam-filled honeycomb core structure.

In yet another particular implementation, a method of manufacturing aduct includes generating a honeycomb core structure having a tubularshape. The honeycomb core structure includes a plurality of hexagonalshaped cavities. The method also includes filling the plurality ofhexagonal shaped cavities of the honeycomb core structure with foam togenerate a foam-filled honeycomb core structure. The method furtherincludes coupling an air-impermeable duct wall to an exterior surface ofthe foam-filled honeycomb core structure.

In a particular implementation, a method of installing a duct on avehicle includes installing the duct in an environmental control systemof the vehicle where the duct includes a foam-filled honeycomb corestructure having a tubular shape and an air-impermeable duct wallcoupled to an exterior surface of the foam-filled honeycomb corestructure.

By using one of the ducts described herein, an environmental controlsystem can more efficiently meet acoustic design requirements, achievebetter thermal performance, achieve a lower weight and volumeconfiguration, and reduce costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates examples of ducts;

FIG. 2 is a block diagram of an aircraft that includes an example of anenvironmental control system including one of the ducts of FIG. 1;

FIG. 3 is a diagram that illustrates a perspective view of an example ofthe environmental control system of FIG. 2;

FIG. 4A is a diagram that illustrates a cross-section view of an exampleof one of the ducts of FIG. 1;

FIG. 4B is a diagram that illustrates a cross-section view of an exampleof another of the ducts of FIG. 1;

FIG. 5A is a diagram that illustrates a side view of an example of theduct of FIG. 4A;

FIG. 5B is a diagram that illustrates a cross-section view of the ductof FIG. 5A;

FIG. 6 is a diagram that illustrates a cross-section view of anotherexample the duct of FIG. 4A;

FIG. 7 is a diagram that illustrates a cross-section view of anotherexample of the duct of FIG. 4A;

FIG. 8A is a diagram that illustrates a cross-section view of an exampleof the duct of FIG. 4B including a sleeve;

FIG. 8B is a diagram that illustrates a cross-section view of an exampleof the duct of FIG. 4B including an internal coupler;

FIG. 9 is a diagram that illustrates a cross-section view of aparticular example of the duct of FIG. 4B;

FIG. 10 is a diagram that illustrates a detailed cross-section view of aduct including an example of an internal coupler;

FIG. 11A is a diagram that illustrates a cross-section view of anexample of a duct including a foam-filled honeycomb core structure;

FIG. 11B is a diagram that illustrates the foam-filled honeycomb corestructure including a plurality of cavities of the duct of FIG. 11A;

FIG. 11C is a diagram that illustrates the foam-filled honeycomb corestructure including foam of the duct of FIG. 11A;

FIG. 11D is a diagram that illustrates the foam-filled honeycomb corestructure and an air-impermeable duct wall of the duct of FIG. 11A;

FIG. 12A is a diagram that illustrates a cross-section view of anexample of the duct of FIG. 11A including an interior layer;

FIG. 12B is a diagram that illustrates a particular example of the ductof FIG. 12A;

FIG. 12C is a diagram that illustrates another example of the duct ofFIG. 12A;

FIG. 12D is a diagram that illustrates another example of the duct ofFIG. 12A;

FIG. 13 is a diagram that illustrates an example of perforations of arigid tube of a duct;

FIG. 14 is a flow chart of an example of a method of manufacturing aduct;

FIG. 15 is a flow chart of another example of a method of manufacturinga duct;

FIG. 16 is a flow chart of another example of a method of manufacturinga duct;

FIG. 17 is a flow chart of an example of a method of duct manufacturingand service;

FIG. 18 is a block diagram that illustrates an example of a vehicleincluding a duct; and

FIG. 19 is a diagram that illustrates a top view of an example of anaircraft including the environmental control system of FIG. 2.

DETAILED DESCRIPTION

The disclosed embodiments provide ducts that absorb sound for use inenvironmental control systems. Methods of manufacturing the ducts arealso disclosed. A duct according to particular aspects discloses hereincan function as a noise attenuating muffler and can reduce the use ofdedicated noise attenuating mufflers in an environmental control system.For example, conventional ducts and noise attenuating mufflers may bereplaced with the disclosed ducts.

In a first implementation, a first duct (e.g., a first type of duct)includes a rigid air-permeable tube of composite material forming aninterior surface or wall of the first duct. The first duct also includesa layer of insulation (e.g., foam or felt) and a non-rigid outer liner.The non-rigid outer liner seals the ducts to form an air-impermeableduct wall and provides an outer layer or second layer of thermal andsound insulation. As compared to conventional ducts which include arigid outer wall (or a rigid outer wall wrapped in non-rigid thermalinsulation), the first duct includes a non-rigid outer liner that sealsthe duct and provides thermal insulation (and some sound absorption). Ascompared to conventional ducts, the first duct is lighter and lessexpensive to produce.

In a second implementation, a second duct (e.g., a second type of duct)includes a rigid tube of composite material and an insulation layerdisposed within the rigid tube. The second duct further includes abiasing member (e.g., a spring) disposed within the rigid tube whichsecures the insulation layer against an interior surface of the rigidtube. Similar to the first duct, the second duct has one rigidcomponent, i.e., the outer layer or tube. Conventional ducts often havetwo or more rigid components. Accordingly, as compared to conventionalducts, the second duct is lighter and less expensive to produce.

In a third implementation, a third duct (e.g., a third type of duct)includes a foam-filled honeycomb core structure having a tubular shapeand an air-impermeable duct wall coupled to an exterior surface of thefoam-filled honeycomb core structure. The foam-filled honeycomb corestructure includes a plurality cavities filled with foam. Theair-impermeable duct wall (e.g., thermoplastic film or rigid compositetube) is coupled to the foam-filled honeycomb core structure to seal thethird duct. In some implementations, the third duct further includes aninterior layer. For example, the third duct further includes a rigidair-permeable tube of composite material or a layer of foam as theinterior layer. As compared to conventional ducts, the third duct isstronger and lighter because its “insulation layer,” the foam-filledhoneycomb core structure, provides structural support and stability. Thefoam-filled honeycomb core structure enables the air-impermeable ductwall to be a non-rigid outer liner (e.g., thermoplastic film) or arelatively thin layer of composite material (as compared to conventionalducts where the outer layer provides structural stability). For example,the composite material may be only one or two plies thick.

A technical effect of embodiments described herein enable anenvironmental control system to be lighter, smaller, or less expensivethan other ducts not having at least some of these features.Accordingly, vehicles that include such environmental control system canbe lighter, smaller, and less expensive.

FIG. 1 illustrates a block diagram 100 of examples of ducts 102. Theducts 102 may be include in an environmental control system, such as anenvironmental control system 202 of FIG. 2. The ducts 102 may beincluded in a vehicle, such as the aircraft 200 of FIG. 2.

The duct 102A includes a rigid air-permeable tube of composite material112 (also referred to herein as a rigid air-permeable tube 112), a layerof insulation 114, and a non-rigid insulation layer 116. The rigidair-permeable tube of composite material 112 includes or corresponds totube of composite material formed from “open” weave composite materialor a rigid perforated tube 136. Open weave composite materials includecomposite material having an arrangement or pattern of fibers that isopen loop. Examples of open loop arrangements include a leno weavearrangement (a.k.a., a gauze weave or cross weave arrangement). The lenoweave arrangement is a type of plain weave in which adjacent “warp”fibers are twisted around consecutive “weft” fibers to form a spiralpair, effectively ‘locking’ each weft in place. An open weave compositematerial tube 132 includes (e.g., is formed from) a few plies of openweave composite material such that when the open weave compositematerial is cured the open weave composite material tube 132 containsopenings in which air can pass through (i.e., is air-permeable). The airpermeability of the open weave composite material tube 132 enables theduct 102A to absorb sound like a noise attenuating muffler.

The rigid perforated tube 136 includes a plurality of perforations(e.g., perforations 1312 of FIG. 13) such that air can pass through theperforations and the rigid perforated tube 136. In some implementations,the rigid perforated tube 136 includes or corresponds to a tube ofcomposite material formed from “closed” weave composite materials.

The layer of insulation 114 is coupled to an exterior surface of therigid air-permeable tube 112 and comprises a middle layer of the duct102A. The layer of insulation 114 is configured to provide thermalinsulation and/or sound absorption. The layer of insulation 114 includesa layer of foam or felt. As illustrative, non-limiting examples, thelayer of insulation 114 includes open cell foam 152 or aramid felt 154.

In some implementations, the open cell foam 152 has a spiral wrappedconfiguration. To illustrate, the open cell foam 152 is in strips ortriangles and is wrapped around the exterior of the rigid air-permeabletube of composite material 112. As an illustrative, non-limitingexample, the open cell foam 152 includes or corresponds to melaminefoam. The aramid felt 154 includes aramid fibers, such as meta-aramidfibers, para-aramid fibers, or a combination thereof, which are matted,condensed, and/or pressed together. As an illustrative, non-limitingexamples, the aramid felt 154 may include or correspond to a meta-aramidfelt (e.g., a Nomex felt material—Nomex is a registered trademark ofDuPont) or a para-aramid felt.

The non-rigid insulation layer 116 is in contact with the layer ofinsulation 114, and the non-rigid insulation layer 116 forms anair-impermeable duct wall. The non-rigid insulation layer 116 isconfigured to provide thermal insulation and to seal the duct 102A. Insome implementations, the non-rigid insulation layer 116 absorbs sound.The non-rigid insulation layer 116 includes or corresponds to a layer ofthermoplastic film 162 or a layer of high mass fabric 164 that acts asan outer liner of the duct 102A. The layer of thermoplastic film 162 mayinclude a polyetherketoneketone (PEKK) film, a polyether ether ketone(PEEK) film, a Poly Vinyl Fluoride (PVF), a non-flammable materialpressure-sensitive tape, or a combination thereof (e.g., a first layerof PEKK film and a second layer of PEEK film). In some implementations,the layer of thermoplastic film 162 includes one to two plies or layersof thermoplastic material. The high mass fabric 162 as used hereinincludes materials made of natural or synthetic fibers that produce afabric having an areal density (a.k.a., basis weight) greater than about15 ounces per square yard. Such an areal density provides sound blocking(e.g., reducing or preventing breakout noise through a cross section ofthe duct), thermal insulation, and can act as an air-impermeable liner.

The duct 102B includes a biasing member 122, an insulation layer 124,and a rigid tube of composite material 126. The rigid tube of compositematerial 126 is configured to support the duct 102B. The rigid tube ofcomposite material 126 may include or correspond an arrangement ofcomposite material that is non-permeable and forms an air-impermeableexterior duct wall.

The biasing member 122 is disposed within the rigid tube of compositematerial 126 and is configured to restrain the insulation layer 124within the rigid tube of composite material 126. For example, thebiasing member 122 exerts a force (e.g., a radially outward force) thatsecures and restrains the insulation layer 124 against an interiorsurface of the rigid tube of composite material 126. In someimplementations, the biasing member 122 includes or corresponds to aspring, such as the spring 822 of FIG. 8. As an illustrative,non-limiting example, the biasing member 122 is a helical compressionspring.

The insulation layer 124 is configured to absorb sound and providethermal insulation. The insulation layer 124 includes the open cell foam152, the aramid felt 154, the high mass fabric 164, or a combinationthereof. As an illustrative, non-limiting example the insulation layer124 includes a layer of Nomex felt.

The duct 102C includes a foam-filled honeycomb core structure 144 and anair-impermeable duct wall 146. The foam-filled honeycomb core structure144 has a tubular shape. To illustrate, the foam-filled honeycomb corestructure 144 defines an inlet and an outlet opposing the inlet. Thefoam-filled honeycomb core structure 144 has an interior surface and anexterior surface that opposes the interior surface. The foam-filledhoneycomb core structure 144 includes a core structure 172 that definesa plurality of cavities 174, as depicted in FIGS. 11B-11D. Thefoam-filled honeycomb core structure 144 includes foam 176 within theplurality of cavities 174. The foam 176 may include or correspond to theopen cell foam 152, a closed cell foam 134, or a combination thereof.

The air-impermeable duct wall 146 is coupled to an exterior surface ofthe foam-filled honeycomb core structure 144. The air-impermeable ductwall 146 is configured to seal the duct 102C. The air-impermeable ductwall 146 may be flexible or rigid. For example, the air-impermeable ductwall 146 may include or corresponds to a layer of the thermoplastic film162, a layer of the high mass fabric 164, or a rigid tube 166. The rigidtube 166 can be made from composite materials, plastic, metal, of acombination there.

In some implementations, the duct 102C further includes an interiorlayer coupled to an interior surface of the foam-filled honeycomb corestructure 144. For example, the duct 102C further includes the openweave composite material tube 132, a layer of closed cell foam 134, orthe rigid perforated tube 136 coupled to the interior surface of thefoam-filled honeycomb core structure 144.

In some implementations, the ducts 102A-102C include adhesive material,such as the adhesive material 522 of FIG. 5, to couple a first duct to asecond duct or another component via coupler, such as a sleeve 512 ofFIG. 5 or an internal coupler 812 of FIG. 8, as further describedherein. Additionally or alternatively, the duct 102A includes adhesivetape, such as adhesive tape 622 of FIG. 6, coupled to the layer ofinsulation 114, to the non-rigid insulation layer 116, or to both. Inaddition, the duct 102B may include adhesive tape, such as the adhesivetape 622 of FIG. 6, coupled to the insulation layer 124. The ducts102A-102C may be manufactured by exemplary methods of manufacturingdescribed with reference to FIGS. 14-16.

In operation, the ducts 102A-102C are configured to transport treatedair, provide thermal insulation, provide sound absorption, provide soundblocking, and provide structural integrity for positive and negativepressure applications. Operation of the ducts 102A-102C are describedfurther with reference to FIG. 3.

FIG. 2 is a block diagram of an aircraft 200 that includes an example ofan environmental control system (ECS) 202 which includes one of theducts 102A-102C of FIG. 1. In other implementations, the ECS 202 isincluded on other vehicles, such as a rocket, a helicopter, a car, abus, a train, a ship, a submarine, etc.

As illustrated in FIG. 2, the ECS 202 includes a duct system 212, an airconditioning unit 214, an intake port 222, and an exhaust port 224. Theduct system 212 is configured to provide treated fluid (e.g., treatedair 352 of FIG. 3) to passengers of the aircraft 200. The duct system212 includes or more ducts. As illustrated in FIG. 2, the duct system212 includes first zone ducts 232, riser ducts 234, second zone ducts236, and outlet ports 238.

One or more of the first zone ducts 232, the riser ducts 234, and thesecond zone ducts 236 may include the ducts 102A-102C of FIG. 1. Asillustrated in the implementation of FIG. 2, the first zone ducts 232include at least one of the ducts 102A-102C of FIG. 1. The first zoneducts 232, the riser ducts 234, and the second zone ducts 236 areconfigured to transport fluid through the duct system 212.

The outlet ports 238 are configured to provide the fluid to thepassengers. For example, the outlet ports 238 include or correspond tocabin or passenger vents. The outlet ports 238 may be controllable(e.g., opened or closed) by the passengers. The outlet ports 238 may becoupled to the first zone ducts 232, the riser ducts 234, the secondzone ducts 236, or a combination thereof.

The air conditioning unit 214 is in fluid communication with the ductsystem 212 and is configured to condition or treat fluid (e.g., air)within the ECS 202. The intake port 222 is in fluid communication withthe duct system 212 and is configured to intake or receive fluid (e.g.,air) into the ECS 202. For example, the intake port 222 may intake fluidfrom within the aircraft 200 (e.g., a pressurized compartment and/orcabin of the aircraft 200) or from outside the aircraft 200 (e.g.,ambient or unpressurized air).

The exhaust port 224 is in fluid communication with the duct system 212and is configured to exhaust or expend fluid (e.g., air). For example,the exhaust port 224 may exhaust fluid outside of the aircraft 200 orout of the ECS 202 (e.g., exhaust to fluid to a filter or another systemof the aircraft 200). Although the ECS 202 of FIG. 2 includes the airconditioning unit 214, in other implementations the ECS 202 may includeother components (e.g., a heater, electrical equipment, an exhaustsystem, a fan, orifices, etc., or a combination thereof) in addition toor in the alternative of the air conditioning unit 214. Operation of theECS 202 of FIG. 2 is described with reference to FIG. 3.

FIG. 3 is a diagram 300 that illustrates a particular example of theenvironmental control system (ECS) 202 of FIG. 2. In FIG. 3, the firstzone ducts 232 are located below a cabin 312 (e.g., in an area 314 belowa floor 322 of the cabin 312) of the aircraft 200, the riser ducts 234are located between the cabin 312 and an exterior (e.g., skin) of theaircraft 200, the second zone ducts 236 are located above a ceiling 324of the cabin 312 (e.g., in a crown 316 of the aircraft 200).

During operation, treated air 352 from the air conditioning unit 214(and/or the intake port 222) is received by the first zone ducts 232.The first zone ducts 232 transport the treated air 352 through the firstzone ducts 232 and to the riser ducts 234. As the treated air 352 movesthrough the first zone ducts 232, the treated air 352 generates noise.Additionally or alternatively, noise is generated by fans, ductgeometry, flow control devices, object in a flow path of the treated air352, or a combination thereof. The first zone ducts 232 attenuate thenoise and provide thermal insulation such that heat of ambient air(e.g., air external to the ECS 202) is not transferred to the treatedair 352 and that heat of the treated air 352 is not transferred to theambient air.

The riser ducts 234 transport the treated air 352 through the riserducts 234 and to the second zone ducts 236. In some implementations, theriser ducts 234 also transport the treated air 352 to the outlet ports238, where the treated air 352 can be controlled by passengers. As thetreated air 352 moves through the riser ducts 234, the treated air 352generates noise. The riser ducts 234 attenuate the noise and providethermal insulation.

The second zone ducts 236 transport the treated air 352 through thesecond zone ducts 236 and to air conditioning unit 214 (and/or exhaustport 224). In other implementations, the second zone ducts 236 transportthe treated air 352 to the outlet ports 238, where the treated air 352can be controlled by passengers. As the treated air 352 moves throughthe second zone ducts 236, the treated air 352 generates noise. Thesecond zone ducts 236 attenuate the noise and provide thermalinsulation.

As illustrated in FIG. 3, the exemplary ECS 202 is free of distinctnoise attenuating mufflers (e.g., zone mufflers). For example, the ECS202 does not include duct sections that have external noise attenuatingmufflers encasing the duct sections and/or duct and dedicated noiseattenuating muffler combination sections configured to absorb soundabove or below the cabin 312, as in a conventional ECS.

FIGS. 4A and 4B illustrate a cross-section view of an example of theduct 102A and an example of the duct 102B. In FIGS. 4A and 4B, theexamples of the ducts 102A and 102B are curved. In other examples, suchas in FIGS. 5 and 8, the ducts 102A-102C are straight. In FIG. 4A, theduct 102A includes the rigid air-permeable tube 112, the layer ofinsulation 114, the non-rigid insulation layer 116. In FIG. 4B, the duct102B includes the biasing member 122, the insulation layer 124, and therigid tube of composite material 126. Additional examples of the ducts102A and 102B are illustrated in FIGS. 5A, 5B, 6, 7, 8A, 8B, 9, and 10.

FIGS. 5A and 5B illustrate a side view and a cross-section view (e.g., alongitudinal cross-section) of a particular example of the duct 102A. InFIGS. 5A and 5B, the duct 102A includes the rigid air-permeable tube112, the layer of insulation 114, the non-rigid insulation layer 116,and a sleeve 512. The sleeve 512 is coupled to an exterior surface ofthe rigid air-permeable tube 112 via adhesive material 522. The sleeve512 is configured to overlap a portion of an end of the rigidair-permeable tube 112 of the duct 102A and to overlap a portion of anend of a second duct 102A to couple the duct 102A and the second duct102A in fluid communication.

The adhesive material 522 includes a material configured to bond thesleeve 512 to the rigid air-permeable tube 112. For example, theadhesive material 522 includes silicone or a pressure sensitiveadhesive. As an illustrative, non-limiting example, the adhesivematerial 522 includes Room-Temperature-Vulcanizing (RTV) silicone. Asillustrated in FIG. 5A, the adhesive material 522 is in contact with therigid air-permeable tube 112, which extends past the layer of insulation114 and the non-rigid insulation layer 116.

As illustrated in FIG. 5A, the sleeve 512 is smaller (e.g., has asmaller diameter) than the duct 102A (e.g., a diameter of the non-rigidinsulation layer 116 thereof). In other implementations, the sleeve 512is the same size as or is larger than the duct 102A (e.g., the diameterof the non-rigid insulation layer 116 thereof).

FIG. 5B depicts the cross-section view (e.g., a longitudinalcross-section) of the duct 102A of FIG. 5A. In FIG. 5B, an area 532represents a portion of the duct 102A where adhesive tape, such as theadhesive tape 622 of FIG. 6, can be used to seal the joints or couplingsbetween ducts 102A. For example, the adhesive tape (not shown) can beused to seal the edges between the ducts 102A and the sleeve 512, asfurther described with reference to FIG. 6. In other implementations,the duct 102A includes an internal coupler, such as internal coupler 812of FIG. 8, to couple to a second duct 102A, as described with referenceto FIGS. 8 and 10.

FIG. 6 is a diagram 600 that illustrates a cross-section view (e.g., atransverse or circumferential cross-section) of another example of theduct 102A. In FIG. 6, the duct 102A includes the open weave compositematerial tube 132 for the rigid air-permeable tube 112, a layer of thearamid felt 154 for the layer of insulation 114, and a layer of thethermoplastic film 162 for the non-rigid insulation layer 116. In theexample illustrated in FIG. 6, the layer of aramid felt 154 includes oneply of the Nomex felt and the layer of the thermoplastic film 162includes one or two layers (e.g., plies) of a PEEK film.

The layer of the aramid felt 154 and the layer of the thermoplastic film162 each form a seam 612. For example, the aramid felt 154 is wrappedaround the open weave composite material tube 132 and creates the seam612, and the thermoplastic film 162 is wrapped around the layer ofaramid felt 154 and creates a seam 612.

In FIG. 6, the duct 102A further includes the adhesive tape 622positioned proximate to (e.g., over) the seams 612. The adhesive tape622 is configured to restrain the layer of insulation 114 (i.e., thelayer of aramid felt 154), the non-rigid insulation layer 116 (i.e., thelayer of thermoplastic film 162), or both. In some implementations, theadhesive tape 622 includes or corresponds to pressure sensitive tape. Asan illustrative, non-limiting example, the adhesive tape 622 includes ametalized polyether ether ketone (MPEEK) material. In otherimplementations, the non-rigid insulation layer 116 includes a layer ofthe high mass fabric 164. For example, the non-rigid insulation layer116 includes one to two layers (e.g., plies) of the high mass fabric 164wrapped around the layer of the aramid felt 154.

FIG. 7 is a diagram 700 that illustrates a cross-section view (e.g., atransverse or circumferential cross-section) of another example of theduct 102A. In FIG. 7, the duct 102A includes the open weave compositematerial tube 132 for the rigid air-permeable tube 112, a layer of theopen cell foam 152 for the layer of insulation 114, and a layer of thethermoplastic film 162 for the non-rigid insulation layer 116. In theexample illustrated in FIG. 6, the layer of the open cell foam 152includes a layer of spiral wrapped melamine foam and the layer of thethermoplastic film 162 includes one or two layers (e.g., plies) of aPEEK film. In some implementations, the layer of spiral wrapped melaminefoam includes multiple plies (e.g., three to four plies) of compressedmelamine foam that is wrapped around the open weave composite materialtube 132 in a spiral.

As compared to the duct 102A of FIG. 6 that includes the layer of thearamid felt 154, the duct 102A of FIG. 7 includes the layer of open cellfoam 152. The layer of open cell foam 152 provides higher thermalresistance as compared to the aramid felt 154 or Nomex foam. Open cellfoam 152 provides similar sound absorption to the aramid felt 154 atless cost and weight. The aramid felt 154 provides higher soundabsorption (e.g., absorption and reduction of breakout noise) andtransmission loss (e.g., noise reduction from an inlet of the duct 102Ato an outlet of the duct 102A), as compared to a similar mass of theopen cell foam 152.

FIGS. 8A and 8B each illustrate a cross-section view (e.g., alongitudinal cross-section) of an example of the duct 102B including acoupler. In FIGS. 8A and 8B the duct 102B includes a spring 822 for thebiasing member 122, a layer of the aramid felt 154 for the insulationlayer 124, and the rigid tube of composite material 126. In the exampleillustrated in FIGS. 8A and 8B, the spring 822 includes a helicalcompression spring and the layer of aramid felt 154 includes one ply ofthe Nomex felt.

Referring to FIG. 8A, a first example of the duct 102B including thesleeve 512 is illustrated. In FIG. 8A, the sleeve 512 (e.g., an externalcoupler) is in contact with an exterior of the duct 102B, that is anexterior surface of the rigid tube of composite material 126, as opposedto the sleeve 512 of FIG. 5A that is in contact with the exteriorsurface of the rigid air-permeable tube of composite material 112 of theduct 102A.

In FIG. 8B, a second example of the duct 102B includes an internalcoupler 812. In some implementations, the internal coupler 812 includesthreads (not shown), a bead 814, or a combination thereof, to couple andsecure sections of ducts 102B together. As illustrated in FIG. 8B, theinternal coupler 812 includes the bead 814 (e.g., a protrusion) whichengages with a surface (internal surface) of a second duct 102B or asleeve 512. The bead 814 exerts force to keep the ducts 102B togetherand generates friction which oppose the ducts 102B from decoupling. Forexample, the bead 814 exerts a force on the sleeve 512 that is coupledto the ducts 102B by a hose clamp or a plastic zip tie. The internalcoupler 812 is described further with reference to FIG. 10.

Although, the ducts 102B are shown with two sleeves 512 or two internalcouplers 812 in FIGS. 8A and 8B, in other implementations, a particularduct (e.g., one of the ducts 102A-102C) can include one sleeve 512 andone internal coupler 812.

FIG. 9 is a diagram 900 that illustrates a cross-section view (e.g., atransverse or circumferential cross-section) of a particular example ofthe duct 102B. In FIG. 9, the duct 102B includes the spring 822 for thebiasing member 122, a layer of the aramid felt 154 for the insulationlayer 124, and the rigid tube of composite material 126. In the exampleillustrated in FIG. 9, the layer of aramid felt 154 includes one ply ofthe Nomex felt.

FIG. 10 is a diagram 1000 that illustrates a detailed cross-section view(longitudinal cross-section) of the internal coupler 812 of FIG. 8. InFIG. 10, the internal coupler 812 is a “reducer,” i.e., the internalcoupler 812 reduces an outside diameter 1012, 1014 of the ducts 102B. Toillustrate, a first outside diameter 1012 of the first duct 102B islarger than a second outside diameter 1014 of an interior portion of theinternal coupler 812 (and of a second duct 102B which is coupled to theducts 102B via the internal coupler 812. An exterior portion (e.g., aportion near the bead 814) of the internal coupler 812 has an outsidediameter, a third outside diameter 1016, that is less than the firstoutside diameter 1012 of the first duct 102B and the second outsidediameter 1014 of the interior portion of the internal coupler 812. Insome implementations, the second duct 102B and/or a sleeve (e.g., thesleeve 512) is coupled to internal coupler 812 and contacts the bead814. The second duct 102B and/or the sleeve 512 may be secured to thefirst duct 102B by a hose clamp or a plastic zip tie.

In FIG. 10, an inside diameter 1018 of the duct 102B and the second duct102B remains the same. In other implementations, the internal coupler812 has an inside diameter 1018 that is smaller than the inside diameter1018 of the duct 102B and the internal coupler 812 reduces the insidediameter 1018 of the second duct 102B in addition or in the alternativeto reducing the first outside diameter 1012 of the ducts 102B. Theinternal coupler 812 includes a polymer, a composite material, a metal,or a combination thereof.

FIGS. 11A-11D illustrate a particular example of the duct 102C and thefoam-filled honeycomb core structure 144 thereof. FIG. 11A is a diagramthat illustrates a cross-section view of the duct 102C. In FIG. 11A, theduct 102C has the foam-filled honeycomb core structure 144 and theair-impermeable duct wall 146. The foam-filled honeycomb core structure144 includes the plurality of cavities 174, as illustrated in FIG. 11B.

FIG. 11B depicts surfaces of the foam-filled honeycomb core structure144 defining the plurality of cavities 174. The plurality of cavities174 have a hexagonal shape (e.g., a honeycomb shape). In otherimplementations, one or more of the plurality of cavities 174 have othershapes, such as a circular shape, a rectangular shape, a square shape, apentagonal shape, an octagonal shape, another shape that may betessellated, or a combination thereof. The plurality of cavities 174 areillustrated in FIG. 11B as extending through the foam-filled honeycombcore structure 144, i.e., the plurality of cavities 174 correspond tothrough holes and are defined by both surfaces of the foam-filledhoneycomb core structure 144. In other implementations, the plurality ofcavities 174 do not extend through the foam-filled honeycomb corestructure 144. In a particular implementation, each of the surfaces ofthe foam-filled honeycomb core structure 144 defines a correspondingplurality of cavities 174.

FIG. 11C depicts the foam 176 in the plurality of cavities 174 of thefoam-filled honeycomb core structure 144. As illustrated in FIG. 11C,the foam 176 (e.g., the closed cell foam 134 or the open cell foam 152extends to the surfaces of the foam-filled honeycomb core structure 144.In other implementations, the foam 176 terminates before or extends pastthe surfaces of the foam-filled honeycomb core structure 144. The foam176 may be grown in-situ (i.e., within the plurality of cavities 174) ormay be inserted into the plurality of cavities 174.

The foam-filled honeycomb core structure 144 (e.g., portions thereof)includes one or more layers (e.g., the air-impermeable duct wall 146)coupled to the surfaces of the foam-filled honeycomb core structure 144that define the plurality of cavities 174, as illustrated in FIG. 11D.In a particular implementation, the air-impermeable duct wall 146includes composite material.

FIG. 12A illustrates a cross-section view of an example of the duct 102Cincluding an interior layer. In FIG. 12A, the duct 102C includes thefoam-filled honeycomb core structure 144, the air-impermeable duct wall146, and one of the interior layers described with reference to FIG. 1.For example, the duct 102C includes one of the open weave compositematerial tube 132, the layer of closed cell foam 134, or the rigidperforated tube 136.

FIG. 12B depicts an example of the duct 102C of FIG. 12A the foam-filledhoneycomb core structure 144 positioned (e.g., sandwiched) between twolayers. In FIG. 12B, the foam-filled honeycomb core structure 144 ispositioned between the open weave composite material tube 132 and alayer of the thermoplastic film 162.

FIG. 12C depicts another example of the duct 102C of FIG. 12A where thefoam-filled honeycomb core structure 144 is positioned between the layerof closed cell foam 134 and a layer of the thermoplastic film 162.

FIG. 12D depicts another example of the duct 102C of FIG. 12A where thefoam-filled honeycomb core structure 144 is positioned between the rigidperforated tube 136 and a layer of the thermoplastic film 162.

FIG. 13 is a diagram 1300 that illustrates an example of theperforations 1312 of the rigid tube 166 of the duct 102C. As illustratedin FIG. 13, the duct 102C is curved and the perforations 1312 have acircular cross-section. In other implementations, the duct 102C isstraight and/or the perforations 1312 have a cross-section that isnon-circular, such as an elliptical cross-section, a rectangularcross-section, a square cross-section, a triangular cross-section, or ahexagonal cross-section. In some implementations, the perforations 1312are arranged in a pattern. For example, the perforations 1312 can bearranged in an asymmetrical pattern or a symmetrical pattern. Toillustrate, when the perforations 1312 are symmetrical, the perforations1312 may be symmetrical with respect to an axis or curvature of the duct102C.

The perforations 1312 are configured to allow air and/or sound waves topass from an interior of the rigid tube 166 to another layer of the duct102C. The perforations 1312 of the rigid tube 166 enable the duct 102Cto function similar to a muffler, i.e., to reduce sound generated by airmoving through the duct 102C and an ECS. To illustrate, as a sound wavepropagates to the perforations 1312, a portion of the sound wave passesthrough the perforations 1312 to an insulation layer or material of theduct 102C where it is absorbed.

In some implementations, the perforations 1312 are sized to causedestructive interference (i.e., reduce noise by canceling out soundwaves generated by the air moving through duct 102C). To illustrate,when the sound wave propagates to the perforations 1312, another portionof the sound wave is reflected back into the interior of the rigid tube166. The other portion of the sound wave may cause destructiveinterference with another sound wave and may cancel out at least aportion of the other sound wave. A size of the perforations 1312 isbased on a size (e.g., length and/or diameter) of the rigid tube 166, aspeed of the air, a pressure of the air, or a combination thereof.

FIG. 14 illustrates a particular example of a method 1400 ofmanufacturing a duct, such as the ducts 102A of FIG. 1. The method 1400includes, at 1402, applying insulation to an exterior surface of a rigidair-permeable tube of composite material to form a layer of insulationon the exterior surface of the rigid air-permeable tube. For example,the layer of insulation may include or correspond to the layer ofinsulation 114, the open cell foam 152, or the aramid felt 154 ofFIG. 1. The rigid air-permeable tube of composite material may includeor correspond to the rigid air-permeable tube of composite material 112of FIG. 1. To illustrate, the layer of insulation 114 is formed bywrapping insulation (e.g., the open cell foam 152, the aramid felt 154,or both) around the outside or exterior of the rigid air-permeable tubeof composite material 112. In a particular implementation, the compositematerial of the rigid air-permeable tube 112 includes a fabric materialhaving a leno weave arrangement. In a particular implementation, afterthe insulation is applied, a leak check or test is performed on thecombined rigid air-permeable tube and layer of insulation.

The method 1400 further includes, at 1404, applying non-rigid insulationto an exterior surface of the layer of insulation to form a non-rigidinsulation layer in contact with the layer of insulation, the non-rigidinsulation layer forming an air-impermeable duct wall. For example, thenon-rigid insulation layer may include or correspond to the non-rigidinsulation layer 116, the thermoplastic film 162, or the high massfabric 164 of FIG. 1. To illustrate, the non-rigid insulation layer isformed by is wrapping the non-rigid insulation (e.g., the thermoplasticfilm 162 or the high mass fabric 164) around the outside or exterior ofthe layer of insulation 114.

In some implementations, the rigid air-permeable tube comprises a rigid,perforated tube of composite material. In such implementations, themethod 1400 includes, prior to applying 1402 the insulation to theexterior surface of a rigid air-permeable tube, generating 1412 therigid, perforated tube. In some such implementations, generating 1412includes curing 1422 the composite material into a rigid tube andgenerating 1424 perforations in the rigid tube to form the rigid,perforated tube. To illustrate, composite material is applied to anexterior surface of a tubular tool or mandrel and the composite materialis cured to form the rigid tube by applying heat, light, pressure(plenum pressure or vacuum pressure), or a combination thereof to thecomposite material. Perforations are generated in the rigid tube bymachining the rigid tube to form the rigid, perforated tube of compositematerial.

In other implementations, generating 1412 includes applying thecomposite materials onto a tool to form the rigid, perforated tube suchthat the perforations are formed during curing of the compositematerials. For example, a tool used as the layup surface for thecomposite materials includes protrusions such that the when thecomposite material is cured, the protrusions case perforations in therigid, perforated tube.

In some implementations, the method 1400 further includes, at 1414,applying adhesive tape to the layer of insulation, the non-rigidinsulation layer, or both, to secure the layer of insulation to therigid air-permeable tube, to secure the non-rigid insulation layer tothe layer of insulation, or both. For example, the adhesive tapeincludes or corresponds to the adhesive tape 622 of FIG. 6. Toillustrate, 1 ply of MPEEK adhesive tape is placed along the seams 612of the layer of insulation 114 and of the non-rigid insulation layer 116to secure the layers and to seal the duct 102A.

FIG. 15 illustrates another example of a method 1500 of manufacturing aduct, such as the ducts 102B of FIG. 1. The method 1500 includes, at1502, inserting insulation into a rigid tube of composite material toform a layer of insulation within the rigid tube, the layer ofinsulation in contact with an inner surface of the rigid tube. Forexample, the layer of insulation may include or correspond to theinsulation layer 124, the open cell foam 152, the aramid felt 154, orthe high mass fabric 164 of FIG. 1. The rigid tube of composite materialmay include or correspond to the rigid tube of composite material 126 ofFIG. 1. To illustrate, the insulation layer 124 is formed by wrappinginsulation (e.g., the open cell foam 152, the aramid felt 154, the highmass fabric 164, or a combination thereof) around the inside or interiorof the rigid tube of composite material 126.

The method 1500 further includes, at 1504, inserting a biasing memberinto the rigid tube of composite material to secure the layer ofinsulation within the rigid tube. For example, the biasing member mayinclude or correspond to the biasing member 122 or the spring 822 ofFIG. 8. To illustrate, the biasing member 122 is inserted into theinside or interior of the rigid tube of composite material 126 via andinlet or outlet of the rigid tube of composite material 126. In somesuch implementations, the insulation may be coupled or secured to therigid tube of composite material 126 by the adhesive tape 622 or theinsulation may couple to itself by the adhesive tape 622 to form atubular shape and the insulation layer 124.

In some implementations, the method 1500 includes, prior to insertingthe insulation, coupling 1512 the insulation to the biasing member. Toillustrate, the insulation (e.g., the open cell foam 152, the aramidfelt 154, the high mass fabric 164, or a combination thereof) is wrappedaround or applied to the exterior or outside of the biasing member 122to form the insulation layer 124, and then, the combined insulationlayer 124 and the biasing member 122 is inserted into the rigid tube ofcomposite material 126 to form the duct 102B. For example, theinsulation layer 124 and the biasing member 122 are inserted into therigid tube of composite material 126 as a unitary piece. In some suchimplementations, the insulation may be coupled or secured to the biasingmember 122 by the adhesive tape 622. Alternatively, adhesive material522 couples or secures the insulation to the biasing member 122 or thebiasing member 122 (e.g., the spring 822) is threaded through theinsulation to couple or secure the insulation to the biasing member 122.

FIG. 16 illustrates a particular example of a method 1600 ofmanufacturing a duct, such as the ducts 102B of FIG. 1. The method 1600includes, at 1602, generating a honeycomb core structure having atubular shape, the honeycomb core structure including a plurality ofhexagonal shaped cavities. For example, the honeycomb core structure mayinclude or correspond to the core structure 172 of FIG. 1 and theplurality of hexagonal shaped cavities may include or correspond to theplurality of cavities 174. To illustrate, the core structure 172 isformed into a tubular shape and surfaces thereof define the plurality ofcavities 174. As illustrative, non-limiting examples, compositematerials may be cured to form the core structure 172 or metal may bemachined to form the core structure 172.

The method 1600 also includes, at 1604, filling the plurality ofhexagonal shaped cavities of the honeycomb core structure with foam togenerate a foam-filled honeycomb core structure. For example, the foammay include or correspond to the foam 176, the closed cell foam 134, orthe open cell foam 152 of FIG. 1. The foam-filled honeycomb corestructure may include or correspond to the foam-filled honeycomb corestructure 144 of FIG. 1.

In some implementations, filling 1604 the plurality of hexagonal shapedcavities of the honeycomb core structure with foam includes depositing1612 the foam in the plurality of hexagonal shaped cavities. Toillustrate, the foam 176 is inserted or deposited into the plurality ofcavities 174. In other implementations, filling 1604 the plurality ofhexagonal shaped cavities of the honeycomb core structure with foamincludes generating 1614 the foam within the plurality of hexagonalshaped cavities. To illustrate, a coating is applied (e.g., sprayed) tothe plurality of cavities 174 and heat is applied to the coating togenerate or grow the foam 176 in the plurality of cavities 174.

The method 1600 further includes, at 1606, coupling an air-impermeableduct wall to an exterior surface of the foam-filled honeycomb corestructure. For example, the air-impermeable duct wall may include orcorrespond to the air-impermeable duct wall 146, the thermoplastic film162, or the rigid tube 166 of FIG. 1. To illustrate, the air-impermeableduct wall 146 is formed by wrapping the thermoplastic film 162 aroundthe outside or exterior of the foam-filled honeycomb core structure 144.Alternatively, the air-impermeable duct wall 146 is formed by couplingthe rigid tube 166 to the outside or exterior of the foam-filledhoneycomb core structure 144.

In some implementations, the method 1600 further includes coupling 1622closed a rigid perforated tube of composite material to an interiorsurface of the foam-filled honeycomb core structure. To illustrate, therigid perforated tube of composite material is coupled to the interiorsurface of the foam-filled honeycomb core structure 144. In otherimplementations, the method 1600 further includes coupling 1624 closedcell foam to an interior surface of the foam-filled honeycomb corestructure. To illustrate, the closed cell foam 134 is coupled to theinterior surface of the foam-filled honeycomb core structure 144.

The method 1400 of FIG. 14, the method 1500 of FIG. 15, and/or themethod 1600 of FIG. 16 may be initiated or controlled by anapplication-specific integrated circuit (ASIC), a processing unit, suchas a central processing unit (CPU), a controller, another hardwaredevice, a firmware device, a field-programmable gate array (FPGA)device, or any combination thereof. As an example, the method 1400 ofFIG. 14 can be initiated or controlled by one or more processors, suchas one or more processors included in a control system. In someimplementations, a portion of the method 1400 of FIG. 14 may be combinedwith a second portion of one of the method 1500 of FIG. 15 or the method1600 of FIG. 16. Additionally, one or more operations described withreference to FIGS. 14-16 may be optional and/or may be performed in adifferent order than shown or described. Two or more operationsdescribed with reference to FIGS. 14-16 may be performed at leastpartially concurrently.

Referring to FIGS. 17 and 18, examples of the disclosure are describedin the context of a vehicle manufacturing and service method 1700 asillustrated by the flow chart of FIG. 17 and a vehicle 1802 asillustrated by the block diagram 1800 of FIG. 18. A vehicle produced bythe vehicle manufacturing and service method 1700 of FIG. 17, such asthe vehicle 1802 of FIG. 18, may include an aircraft, an airship, arocket, a satellite, a submarine, or another vehicle, as illustrative,non-limiting examples. The vehicle 1802 may be manned or unmanned (e.g.,a drone or an unmanned aerial vehicle (UAV)).

Referring to FIG. 17, a flowchart of an illustrative example of a methodof duct manufacturing and service is shown and designated 1700. Duringpre-production, the exemplary method 1700 includes, at 1702,specification and design of a vehicle, such as a vehicle 1802 describedwith reference to FIG. 18. During the specification and design of thevehicle 1802, the method 1700 may include specifying a design of a duct,such as the one or more of the ducts 102A-102C of FIG. 1. At 1704, themethod 1700 includes material procurement. For example, the method 1700may include procuring materials for one or more of the ducts 102A-102Cof the vehicle 1802.

During production, the method 1700 includes, at 1706, component andsubassembly manufacturing and, at 1708, system integration of thevehicle 1802. The method 1700 may include component and subassemblymanufacturing (e.g., manufacturing one or more of the ducts 102A-102C ofFIG. 1) of the vehicle 1802 and system integration (e.g., coupling oneor more of the ducts 102A-102C of FIG. 1 to one or more components ofthe vehicle 1802, such as components of the ECS 202 of FIG. 2). At 1710,the method 1700 includes certification and delivery of the vehicle 1802and, at 1712, placing the vehicle 1802 in service. Certification anddelivery may include certifying one or more of the ducts 102A-102C ofFIG. 1 by inspection or non-destructive testing. While in service by acustomer, the vehicle 1802 may be scheduled for routine maintenance andservice (which may also include modification, reconfiguration,refurbishment, and so on). At 1714, the method 1700 includes performingmaintenance and service on the vehicle 1802. The method 1700 may includeperforming maintenance and service of the ECS 202 of FIG. 2, such as theduct system 212 or the air conditioning unit 214, or one or more of theducts 102A-102C of FIG. 1. For example, maintenance and service of theduct system 212 may include replacing one or more ducts of the ductsystem 212 with one or more of the ducts 102A-102C. As a particularnon-limiting illustration, performing maintenance and service includesremoving a duct and noise attenuating muffler from the ECS 202 andinstalling one or more of the ducts 102A-102C in the ECS 202 to replacethe duct and the noise attenuating muffler (e.g., a zone muffler).

Each of the processes of the method 1700 may be performed or carried outby a system integrator, a third party, and/or an operator (e.g., acustomer). For the purposes of this description, a system integrator mayinclude without limitation any number of vehicle manufacturers andmajor-system subcontractors; a third party may include withoutlimitation any number of venders, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

Referring to FIG. 18, a block diagram 1800 of an illustrativeimplementation of the vehicle 1802 that includes a duct, such as one ormore of the ducts 102A-102C of FIG. 1. To illustrate, the vehicle 1802may include an aircraft, such as the aircraft 200 of FIG. 2, as anillustrative, non-limiting example. The vehicle 1802 may have beenproduced by at least a portion of the method 1700 of FIG. 17. As shownin FIG. 18, the vehicle 1802 (e.g., the aircraft 200 of FIG. 2) includesan airframe 1818, an interior 1822, and a plurality of systems 1820. Theplurality of systems 1820 may include one or more of a propulsion system1824, an electrical system 1826, an environmental system 1828, or ahydraulic system 1830. The plurality of systems 1820 further includesthe ECS 202. The ECS 202 may be part of the environmental system 1828 orseparate from the environmental system 1828. The ECS 202 includes thefirst zone ducts 232, the riser ducts 234, the second zone ducts 236,and one or more of the ducts 102A-102C. The ducts 102A-102C may bemanufactured by one or more steps of the methods of FIGS. 14-16.

Apparatus and methods included herein may be employed during any one ormore of the stages of the method 1700 of FIG. 17. For example,components or subassemblies corresponding to production process 1708 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while the vehicle 1802 is in service, at 1712 forexample and without limitation. Also, one or more apparatusimplementations, method implementations, or a combination thereof may beutilized during the production stages (e.g., stages 1702-1710 of themethod 1700), for example, by substantially expediting assembly of orreducing the cost of the vehicle 1802. Similarly, one or more ofapparatus implementations, method implementations, or a combinationthereof, may be utilized while the vehicle 1802 is in service, at 1712for example and without limitation, to maintenance and service, at 1714.

FIG. 19 is a diagram 1900 that illustrates a top view of an example ofthe aircraft 200 including the ECS 202 of FIG. 2. With reference to FIG.19, the aircraft 200 comprises a pair of wings 1904 faired into afuselage 1902. Each wing 1904 carries an engine 1906. The fuselage 1902comprises the cabin 312 for passengers and crew. In the presentembodiment, the aircraft 200 includes two air conditioning units 214 toprovide the treated air 352 (i.e., conditioned air) of FIG. 3 to thecabin 312 via the duct system 212.

In the implementation illustrated in FIG. 19, each air conditioning unit214 has a corresponding duct system 212 that extends along a length ofthe cabin 312 fore and aft. The duct system 212 includes the first zoneducts 232, the riser ducts 234, and the second zone ducts 236 of FIG. 2.One or more of the first zone ducts 232, the riser ducts 234, or thesecond zone ducts 236 include one or more of the ducts 102A-102C. Thefirst zone ducts 232, the riser ducts 234, and the second zone ducts 236can be arranged as illustrated in FIG. 3. For example, the first zoneducts 232 receive the treated air 352 from a corresponding airconditioning unit 214 and provide the treated air 352 to the outletports 238, such as via the riser ducts 234 and/or the second zone ducts236. Although two exemplary outlet ports 238 are illustrated in FIG. 19,the duct system 212 can include more the two outlet ports 238.

Each air conditioning unit 214 has or is coupled to at least one exhaustport 224 for outputting waste hot air from the air conditioning unit 214overboard to atmosphere. In a particular implementation, each exhaustport 224 includes a corresponding ram air outlet (not shown) located onthe underside of the corresponding wing 102.

In the implementation illustrated in FIG. 19, each air conditioning unit214 has two intake ports 222 for receiving air to be treated anddistributed to the cabin 312 via the duct system 212 and/or waste hotair to be exhausted. In the implementation illustrated in FIG. 19, eachair conditioning unit 214 has an intake port 222A (e.g., a first intakeport) to receive air from the atmosphere and has an intake port 222B(e.g., a second intake port) to receive air from the cabin 312.

The illustrations of the examples described herein are intended toprovide a general understanding of the structure of the variousimplementations. The illustrations are not intended to serve as acomplete description of all of the elements and features of apparatusand systems that utilize the structures or methods described herein.Many other implementations may be apparent to those of skill in the artupon reviewing the disclosure. Other implementations may be utilized andderived from the disclosure, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof the disclosure. For example, method operations may be performed in adifferent order than shown in the figures or one or more methodoperations may be omitted. Accordingly, the disclosure and the figuresare to be regarded as illustrative rather than restrictive.

Moreover, although specific examples have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar results may be substituted forthe specific implementations shown. This disclosure is intended to coverany and all subsequent adaptations or variations of variousimplementations. Combinations of the above implementations, and otherimplementations not specifically described herein, will be apparent tothose of skill in the art upon reviewing the description.

The Abstract of the Disclosure is submitted with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. In addition, in the foregoing Detailed Description, variousfeatures may be grouped together or described in a single implementationfor the purpose of streamlining the disclosure. Examples described aboveillustrate but do not limit the disclosure. It should also be understoodthat numerous modifications and variations are possible in accordancewith the principles of the present disclosure. As the following claimsreflect, the claimed subject matter may be directed to less than all ofthe features of any of the disclosed examples. Accordingly, the scope ofthe disclosure is defined by the following claims and their equivalents.

What is claimed is:
 1. A duct comprising: a foam-filled honeycomb corestructure having a tubular shape; and an air-impermeable duct wallcoupled to an exterior surface of the foam-filled honeycomb corestructure.
 2. The duct of claim 1, wherein the foam-filled honeycombcore structure has a structural honeycomb portion comprising metal,composite material, or a combination thereof and defining a plurality ofcavities.
 3. The duct of claim 2, wherein the foam-filled honeycomb corestructure has foam in the plurality of cavities, and wherein the foam ofthe foam-filled honeycomb core structure comprises open cell foam. 4.The duct of claim 3, wherein the open cell foam includes melamine foam.5. The duct of claim 1, wherein the air-impermeable duct wall comprisesa non-rigid insulation layer.
 6. The duct of claim 5, further comprisingadhesive tape coupled to the non-rigid insulation layer, the adhesivetape configured to restrain and seal the non-rigid insulation layer, andwherein the adhesive tape includes metalized polyether ether ketone(MPEEK).
 7. The duct of claim 1, wherein the air-impermeable duct wallcomprises a rigid tube of composite material.
 8. The duct of claim 7,wherein the composite material comprises a fabric material having a lenoweave arrangement.
 9. The duct of claim 1, wherein the foam-filledhoneycomb core structure further includes an inlet, an outlet opposingthe inlet, and an interior surface opposing the exterior surface, andwherein the foam-filled honeycomb core structure is configured to absorbsound, to thermally insulate the duct, and to structurally support theduct.
 10. The duct of claim 1, further comprising a rigid air permeabletube of composite material or a layer of closed cell foam coupled to aninterior surface of the foam-filled honeycomb core structure.
 11. Avehicle including the duct of claim 1, the vehicle comprising: anenvironmental cooling system, the environmental cooling systemincluding: an air conditioning unit; first zone ducts; second zoneducts; and riser ducts coupled to the first zone ducts and the secondzone ducts, wherein one of the first zone ducts, the second zone ducts,or the riser ducts comprises the duct of claim
 1. 12. The vehicle ofclaim 11, further comprising a fuselage, the fuselage including a cabin,wherein the first zone ducts are located above the cabin in a crown ofthe fuselage, wherein the second zone ducts are located below the cabin.13. The vehicle of claim 12, wherein the first zone ducts includes theduct, and wherein at least one duct of the second zone ducts and atleast one duct of the riser ducts includes a second duct comprising: asecond foam-filled honeycomb core structure having a tubular shape; anda second air-impermeable duct wall coupled to an exterior surface of thesecond foam-filled honeycomb core structure.
 14. The vehicle of claim11, wherein the first zone ducts and the second zone ducts do notinclude zone mufflers.
 15. A method of manufacturing a duct, the methodcomprising: generating a honeycomb core structure having a tubularshape, the honeycomb core structure including a plurality of hexagonalshaped cavities; filling the plurality of hexagonal shaped cavities ofthe honeycomb core structure with foam to generate a foam-filledhoneycomb core structure; and coupling an air-impermeable duct wall toan exterior surface of the foam-filled honeycomb core structure.
 16. Themethod of claim 15, wherein filling the plurality of hexagonal shapedcavities of the honeycomb core structure with the foam includesdepositing the foam in the plurality of hexagonal shaped cavities orgenerating the foam within the plurality of hexagonal shaped cavities.17. The method of claim 15, wherein the air-impermeable duct wallcomprises a non-rigid insulation layer, and further comprising couplinga rigid perforated tube of composite material or closed cell foam to aninterior surface of the foam-filled honeycomb core structure.
 18. Themethod of claim 15, wherein the air-impermeable duct wall comprises arigid tube of composite material, and further comprising coupling arigid perforated tube of composite material or closed cell foam to aninterior surface of the foam-filled honeycomb core structure.
 19. Amethod of installing a duct on a vehicle, the method comprising:installing the duct in an environmental cooling system of the vehicle,the duct comprising: a foam-filled honeycomb core structure having atubular shape; and an air-impermeable duct wall coupled to an exteriorsurface of the foam-filled honeycomb core structure.
 20. The method ofclaim 19, further comprising, prior to installing the duct of claim 1,removing a second duct, a muffler, or a combination thereof, and whereininstalling the duct includes replacing one or more of the second duct,the muffler, or the combination thereof, with the duct of claim 1.